Yosef was sold for 20 silver pieces.
Yerushalmi (Shekalim 2:3) and Bereishis Rabbah (84:18) both say that since the 10 brothers each received 2 silver pieces, which were worth half a shekel, their descendants would later be obligated to give half a shekel as a Kaporah.
The Korban HaEdah on the Yerushalmi explains that Binyomin was not with them, but does not mention Reuven.
Does it say anywhere that the brothers would have split their share of 20 silver coins with Reuven and did Reuven accept his share?
Pirkei DeRebbi Eliezer (38) says that Reuven told his brothers not to kill him, but to throw him into the pit so that he could return later to remove him and save him. It then says that the brothers sold Yosef for 20 silver pieces and each of the brothers took 2 pieces of silver to buy shoes. Reuven however, was not there yet, so it seems they left him 2 silver coins, but did Reuven accept it?